Directive antenna array



Amin 9 94@ w. R. BLAIR 2,196,187

DIRECTIVE ANTENNA ARRAY i Filed Jan. 19, 1937 2 Sheets-Sheet 1 1,14 WAVE ANTENNA L7 Z-J Tj.. Z :ai 11255,@ s CZ pril 9, 1940. w. R. BLAIR 2,196,187

DIRECTIVE ANTENNA ARRAY Filed Jan. 19, 1957 2 Sheets-Sheet 2 To RAolo TRANsnvrTx-:p

EAR-rn M//LL/,4M R. 544/@ Arrow/vens- Patented Apr. 9, 1940 Unirse stares PATENT @FFME 8 Claims.

(Cl. Z50- 11) (Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 0. G. 757) This invention relates to improvements in directive antenna arrays.

An object of the invention is to provide an antenna system adapted to shape and control the angle of elevation with respect to the earths surface either in the transmission or reception of electromagnetic wave energy.

The invention proposes a radiation system having the characteristic of low angle radiation to l control the fading-free range of the ground wave; and it is, therefore, an important object to extend the ground component so that the eiiective day or night range may always be a maximum, with minimum or absence of fading.

Another object is to so change and control the current distribution in a transmitting antenna as to increase the magnitude of the ground wave; and to alter the space characteristics of an antenna array by changing the phase and amplitude of the radio frequency exciting current to produce a desired form of radiated pattern.

Another object is to so adjust and control a receiving antenna. system as to provide for directive reception in the vertical plane and so that preference may be given to the ground component. Other objects will appear as the description proceeds.

The invention will now be described with reference to the accompanying drawings, in which:

Fig. l shows the approximately circular contour of the radiated pattern in the Vertical plane of a conventional vertical antenna, for example, a quarter wave antenna;

Fig. 2 shows the low angle radiated pattern of an antenna system arranged and controlled in accordance with the present invention;

Fig. 3 shows an antenna system arranged and controlled in accordance with the present invention;

Figs. 3al and 3b are diagrams to be considered in connection with Fig. 3 to demonstrate the theory of operation in accordance with the present invention;

Fig. i shows another embodiment of the invention comprising an arrangement of four onesixteenth wave antenna units, which are coupled and fed in accordance with the principles of the invention;

Fig. 5 shows still another embodiment of the invention comprising an arrangement of loop antennas which are coupled and fed in accordance with the principles yof the invention; and

Fig, 6 shows an application of the principles of the invention to obtain directivity by the use of horizontal antennas.

In case of a conventional vertical quarter wave antenna shown in Fig. l, the current distribution being sinusoidal, the contour of the radiated pattern will be approximately circular as shown. Thus, in addition to a strong ground Wave. a 5 considerable portion of the energy is propagated skyward and will eventually be reflected by the ionized layers. If this reiiected component returns to earth within the range of the ground wave, interference and fading will result. It fol- 10 lows, therefore, that if the sky component of the radiated wave be materially reduced in magnitude and elevation, the ground wave will be free from interference and hence a greater reliable range will result. 15

One means of changing the polar inductive characteristics in the vertical plane is to change the current distribution along the length of the antenna, and it is the purpose of this invention to provide such a means of so controlling the 20 magnitude and phase of the current at various heights that the Wave instead of having a radiation pattern as shown in Fig. 1, will have a pattern more nearly of the form shown in Fig. 2. From this it may be seen that owing to the 25 low angle radiation, the ground component is increased at the same time that the reduced sky wave is reflected back to earth beyond the ground range of the transmitter and hence does not produce interference. 30

This alteration of current distribution is accomplished by dividing the antenna into separate units, exciting each unit in proper phase, and varying the magnitude and/or phase of the current in each element so that the distribution re- 35 ferred to in Fig. 2 by way of example is secured.

Embodiments of the invention for attaining the desired results are illustrated in Figs. 3 and e. Fig. 3 shows two one-eighth wave'antennas Al and A2 fed in proper phase to secure the desired 40 characteristic. For the purpose of bringing out the theory of operation, reference is lmade to Fig. 3a, in which P represents a relatively distant point in free space located at distances ri and r2, respectively, from antenna elements AI and A2. 45 In Fig. 3h the voltages received at the point P from each element are represented as vectors el and e2, respectively. Assuming the currents to be in phase, the phase difference between el and e2 is equal to angle e which for the case of two 50 one-eighth Wave antennas is approximately equal to 1r/4 cos 0. Should an antenna. comprising quarter wave units be employed, the phase angle is approximately equal to Tr/i cos 0.' It should be noted that the considerations herein mentioned 55 were assumed for the simplest case where the currents in the two sections or antenna. units. were equal and in phase. Actually the current fed to each one-eighth wave antenna is found to be much greater than with a single one-fourth wave antenna. It is therefore apparent that the field pattern is elongated with a corresponding increase in ground range. Actual eld tests have verified these phenomena.

Referring now more particularly to Fig.` 3, the method of feed and control in accordance with the present invention will be described in detail. An antenna array is shown comprising two 1/3 wave sections Ai and A2, the equal in height of a single 1/4 wave antenna. To secure the desired phase and magnitude control use is made of the fundamental concept of electrical loading. Each antenna section is resonated by the addition of an equivalent 1/8 wave loading coil, the underlying principles of which are well known to the art and no claim is made in this invention for their separate use. In this particular application my invention concerns the feeding of two 1/3 wave antennas by means of loading coils, determining either or both to secure phase and magnitude control thus varying the normally utilized current distribution along said antenna. The two antenna sections AI and A2 are coupled to the exciting source, the transmission line TL, thus loading circuits Ll, CI and L2, C2, respectively, and coupling network L4 and L5. An additional loading circuit L3, C3 common to both sections is included in the ground leg of the network to reduce the losses. Thus, the loading circuits Ll, CI and L2, C2 are tuned to less than V8 wave, the deficient amount being supplied by L3, C3. The circuit L3, C3 is not absolutely necessary for the proper functioning of my, invention since the entire loading for the antenna elements could be taken care of by LI, Ci and L2, C2 if the question of radiation losses is not the major consideration.

In Fig. 4 is shown a further variation of my invention wherein I apply the underlying principle of my invention to a four element antenna array, each section of which is le A in length. Thus, in Fig. 4 the loading circuits LI CI, L2 C2, L3 C3, L4 C4, together with the common loading coil L5 C5 are each in turn made equivalent to g A. Attention is invited to the fact that in this particular array, only the upper 1/4 of the current distribution curve is utilized. Since, however, this phenomena is repeated in each of sections I to 4 inclusive, the eiect is to change the current gradient of the total array comprising the elements Al, A2, A3 and A4. In Fig. 3, il and i2 denote conventional current indicating means; while in Fig. 4.- the characters Il, I2, I3 and I4 designate similar devices.

Fig. 5 illustrates one method of independently exciting two loop antennas of 1/8 wave natural period from the same radio frequency source to secure the advantages of the sectional vertical antenna herein described. Each is coupled to the transmission line by the means indicated. In the case of loop Al the termination consists of loading means Ll, coil LI coupled to L2 in turn tuned by condenser C2. The other end of the feed line comprises coil L5 coupled to L6, the end termination of the radio frequency transmission line. As with the case of two- 1/8 wave vertical antennas, the loading coil L'l is equivalent to M8 causing the loop AI plus this coil to have the current distribution commonly secured with a single loop of M4 but in this case one-half the radiation is suppressed. Loop A2 is similarly fed through loading coils L8, coil L4 coupled to L3 in turn tuned by C3 terminating in L5 as before.

Fig. 6 illustrates the manner of applying the directivity principle to horizontal antennas in which case the improvement secured is merely the restriction of the horizontal angle of radiation. Thus in this gure I make each section AI and A2 equivalent to M8 in physical length and load each by means of the circuits LI Cl, L2 C2 and L5' C3 as previously described for the vertical antenna feed.

Changes, modications and equivalent arrangements are contemplated within the scope of the invention as defined by the appended claims.

I claim:

1. An antenna array for propagating electromagnetic waves comprising an even number of radiating loops vertically stacked one above the other in a common plane; means for electrically loading each loop; and means for equalizing the distribution of power introduced into each loop, said means comprising' tuned resonant elements for independently 'varying the magnitude and phase of current energy fed to each of said loops.

2. An antenna array for propagating electromagnetic waves comprising an even number of radiating loops, said loops being stacked in common vertical plane relative to one another, and the vertical height of each loop being a small multiple of a quarter wave; means for electrically loading each loop; and means comprising tuned reactance elements for controlling the magnitude and phase of current energy fed to each of said loops.

3. An antenna array for propagating electromagnetic waves comprising an even number of radiating loops, said loops being arranged in stacked relation in a vertical plane, and the vertical height of each loop being a relatively small multiple of a quarter wave length; means for electrically loading each loop; and means for controlling the magnitude of current fed to each of said loops.

4. An antenna array comprising a plurality of radiating elements arranged end to end, each element having a free end to be regarded as its top and the opposite end as its base, each of said elements having an electrical length not exceeding 90 and said elements being arranged with a 90" spacing between the top and bottom of adjacent elements; means for electrically loading each element; and means for equalizing the amount of power introduced into each element to effect control of the radiated eld pattern and whereby the currents at the bases of the adjacent elements are in phase, and the current at the top of any element diiers in phase 90 electrically from that in the base of the next adjacent element.

5. An antenna array for propagating electromagnetic waves, comprising a group of radiating conductors in linear relation from end to end, each conductor having a free end to be regarded as its top and the opposite end as its base, each conductor having an electrical length not to exceed 99 and being disposed to secure a 90 separation between the top and bottom of adjacent conductors whereby adjacent conductors are maintained in phase; means including series loading coils for electrically loading each conductor independently; and means for controlling the phase and magnitude of current introduced into each conductor for securing uniform current distribution from end to end of said array and whereby the currents at the bases of the adjacent conductors are in phase, and the current at the top of any conductor diiers in phase 90 electrically from that in the base of the next adjacent conductor.

6. An antenna array for the reception of electrornagnetic wave energy comprising a plurality of single conductors disposed vertically in end t0 end linear relation with one another, each conductor having a free end to be regarded as its top and the opposite end as its base, each conductor constituting a separate section and the sections having a 90 separation between the top and bottom of adjacent conductors; means for electrically loading each conductor; and means for independently controlling the magnitude and phase of voltage of each conductor whereby the currents at the bases of adjacent conductors are in phase and the current at the top of any conductor differs in phase 90 electrically from that in the base of the next adjacent conductor.

7. An antenna array comprising a plurality of single radiating conductors horizontally disposed `in end to end relation to one another and whose total electrical length does not exceed one wave length, each conductor having a free end to be regarded as its top and the opposite end as its base, and said conductors being arranged with a 90 separation between the top and bottom of adjacent conductors; means for electrically loading each conductor; and means comprising tuned reactances for controlling the magnitude and phase of current energy fed to each conductor whereby the currents at the bases of adjacent Conductors are in phase and the current at the top of any conductor diiers in phase 90 electrically from that in the base of the next adjacent conductor.

8. An antenna array comprising a plurality of single radiating elements disposed in linear end to end relation with one another, each element having a free end to be regarded as its top and the opposite end as its base, each element not to exceed an electrical length of 90 and whose total electrical length does not exceed one wave length, and said elements having a 90 separation between the top and bottom of adjacent elements; means for exciting each element in turn; means for electrically loading each element independently of each other; and means for independently controlling the phase and magnitude of current introduced into each separate element for secur ing the desired current distribution from end to end of the array whereby the currents at the bases of adjacent elements are in phase, and the current at the top of any element differs in phase 90 electrically from that in the base of the next adjacent element.

WILLIAM R. BLAIR. 

